Recent advances in microelectronic technologies have resulted in improvements in operating frequency capabilities of specialized electronic devices such as monolithic microwave integrated circuits (MMICs) and other millimeter wave and microwave devices. These devices are well suited for and often utilized in military and commercial applications requiring wireless communication, detection, ranging and guidance at high frequencies.
The performance capabilities of the devices may be compromised by mounting the device into a package or assembly that adds parasitics and degrades the signal characteristics at higher operating frequencies. These assemblies typically allow an electronic device to be mounted within a suitable enclosure while enabling RF input and output (I/O) signals, as well as a DC bias signal, to be communicated through the assembly walls to the device itself, or conversely, from the device to external complimentary circuits. These devices are typically in the form of modules as an increasing use is made of millimeter wave and microwave transceivers and other such devices. Often, these modules are utilized with various transceiver designs having different transmitter and receiver circuits that make use of a number of different MMIC chips or dies.
Prior art RF assemblies of this type, and more specifically the assembly transitions, are often found to have high RF losses, voltage reflections, electrical mismatching and discontinuity inadequacies that exceed acceptable limits and may limit frequency performance capabilities. This often fails to maximize the performance potential of an electronic device or communication system or may degrade device and system performance. Alternatively, expensive cables and/or connectors are designed into the assemblies to preserve the device performance and to preserve the signal characteristics as they travel through the assemblies.
For example, three areas of packaging representative of devices or modules in the microwave and millimeter wave industry are connectorized amplifiers, internally matched field effect transistors (FET), and surface-mount packaged MMICs. Connectorized amplifiers may generally be characterized by their ruggedness. The respective housings generally include coaxial RF connectors (e.g., two if a 2-port device or more if the device is an n-port). These connectors are typically “field replaceable” surface mount assemblies that possess an RF feed-through soldered or brazed into the housing (e.g., bathtub style or separate ringframe). Additionally, in typical prior art assemblies, DC is brought into the respective housing through capacitively coupled feed-throughs that may be soldered or brazed into the housing. Generally, the RF path is connected to other modules through coaxial cable assemblies, and the DC connections are soldered, or connected to other modules through DC cable assemblies. Such an assembly or package is hermetic and in this sense, it may be labeled as “military microwave hardware” with the expense implied therefrom.
Internally Matched FETs generally represent a focus on the commercial sector and, as such, these devices are not expected to endure the conditions required by military applications. These respective assemblies are typically constrained to 1-stage, 2-port devices and are used for high-power devices where the corresponding baseplate material is employed for heat transfer purposes. The FET may be attached to the baseplate to minimize the thermal resistance of the heat path. Generally, a hard ceramic material is employed on the I/Os to provide a power match to the respective device. Bondwires are used to attach the device to the ceramic material, and a tab is generally attached to the ceramic material and extended from the assembly to provide both an RF connection and DC connection. The DC connections are typically gate (−V), drain (+V) and source (ground) connections. Thus, the intended use of such a device is to have a respective assembly contain a printed circuit board (PCB) to accept the internally matched FET. The assembly is then mechanically attached for thermal and electrical grounding, and the RF I/O tabs are soldered to the PCB.
Surface-mount packaged devices generally possess two or more RF ports depending upon the functionality thereof (e.g., amplifiers, mixers, MMICs, FETs, etc.). A typical attachment method is soldering all pins rather than a mechanical attachment means. For devices dissipating significant power, the accepting PCB generally includes plural vias to remove the associated heat. In this example, the package may possess a back-side metal paddle in addition to the pins. Such packages are generally limited in frequency to prevent parasitics from impacting the performance of the internal device. Therefore, improvements to these packages are desired to reduce their associated parasitics and extend their range of unimpaired useful frequencies. Generally, the number of devices in such a package is limited since suppliers desire to target the maximum number of users. An exemplary industry focusing upon multiple chip solutions inside the package is the cell phone and 802.11 card business.
Thus, a continuing need exists for an improved assembly, particularly for microwave and millimeter wave systems operating in higher frequency ranges. As greater uses are made for microwave and millimeter wave modules, it would be advantageous if a unique structure and method could be found that addressed the low cost and performance requirements in the area of millimeter wave and microwave modules without degradation to the technical performance of a respective transceiver, transmitter, or receiver and/or communication system.